Potential associations between the levels of specific micro-organisms in saliva and the level of dental caries prevalence and incidence in a U.S. adolescent population are being investigated. Initial and interim findings indicate that there is a positive correlation between the level of S. mutans and Lactobacillus in saliva and the prevalence and incidence of dental caries in this study population. The initial caries prevalence for participants having high levels of bacteria in saliva were l.5 DMF surfaces higher than that of those having low levels of bacteria in their saliva. There were l.l fewer new DMF surfaces that developed in subjects with low levels of bacteria in their saliva compared with those having high levels of bacteria in their saliva during the first half of the study.